Abstract 2689: Beat-to-beat Variability of QT Intervals Just Before Ventricular Fibrillation Documented by 24-hour Holter Electrocardiogram
Background- Ventricular fibrillation (VF) is the leading cause of sudden cardiac death, whereas the mechanisms of VF are unclear. The quantitative assessment of the instability of the repolarization process has been suggested as a novel alternative to identify proarrhythmic conditions. Experimentally, an increasing beat-to-beat variability of the repolarization has been reported to precede drug-induced ventricular tachyarrhythmias. We therefore examined the beat-to-beat variability of the QT intervals and RR intervals before the onset of VF episodes recorded on a 24-hour Holter electrocardiogram.
Methods- We analyzed 10 VF episodes in 9 patients with ischemic heart disease (age 60±12 years) and compared those to that in age-and sex-matched controls (n=38). The RR and QT intervals were measured from 20 min before the VF initiation using automated QT measurement software (Suzuken, Japan). The RR and QT intervals were measured in controls with the same timing as that in the VF victims. The beat-to-beat variability was determined from the Poincare plots as short-term variability (STV = ∑|Dn+1-Dn|/[number of heart beat during 5 min × 32], where D represents the duration of the RR or QT interval) (Thomsen 2004), and presented every 5 min.
Results- The VF victims exhibited a higher STVQT at 20 min before the VF (16±9 ms vs. 3±3 ms, p=0.03), but had a lower STVRR at 20 min before the VF (14±3 ms vs. 25±5 ms, p<0.05) compared to that in the controls. The STVQT did not change close to the onset of VF (15 min: 17±7, 10 min: 19±8, 5 min: 22±13, p=0.20, by ANOVA), however the STVRR exhibited a progressive decrease during the initiation of VF (15 min: 14±5, 10 min: 9±8, 5 min: 6±3, p=0.04).
Conclusions- A higher STVQT and progressive decrease in the STVRR characterized the initiation of VF. An increased instability of the repolarization process and parasympathetic withdrawal may be associated with human VF.